It will be of great importance for the detection of the cell concentration of bacteria in the fields of microbial fermentation, environmental monitoring, foods quality inspection, etc. Currently, the common bacteria counting method is culture method, including a plate counting method and a MPN method.
The plate counting method is a national standard inspection method for detecting the total number of bacterial colonies (see reference: GB/T 4789.2-2010 Microbiological examination of food hygiene—Detection of aerobic bacterial count [S]), which is a standard method for judging the accuracy of other counting methods. The method is accurate in single colony counting in a dish, however, as the bacterial colonies in the culture dish are uniform in density, it will be subjective and inaccurate in the artificial observation and counting of adhesion colonies. As a whole, the method is complex in operation, long in time consumption, large in error and low in efficiency.
MPN is a diluent culture counting method. The method is suitable for detecting foods with a large number of competitive bacteria and raw materials thereof and untreated food containing a little amount of Staphylococcus aureus. The MPN method is a common indirect counting method. However, there is a certain limitation for such method.
Such culture methods have the defects of long time consumption, strict sterile operation, complex procedures, high labor and large influence by the culture condition.
In order to overcome the defects of the culture method, a plurality of counting methods are widely used. Among these methods, the fluorescence microscope counting method and the flow cytometry counting method are reliable and widely accepted. For the fluorescence microscope counting method, the fluorescence microscope use ultraviolet rays as a light source for irradiating detected objects to make them emit fluorescent light, and then, the shapes, positions and quantity of the objects are observed under the microscope. In the flow cytometry counting method, particles passing through the laser beam are counted via laser. When particles or cells pass through the laser beam, there will be refraction and reflection on light rays. The refraction signal and the reflection signal are recorded by a detector. A peak will be generated as soon as a cell passes through the laser beam, and finally, the number of peaks is recorded.
Although such two methods have the characteristics of quickness and accuracy, equipment is expensive and the cost of using and maintenance is high. Hence, it will have the important value to seek a bacteria counting method with simple and quick operation and low cost.